metamorphic

Banded gneiss pebble

Gneiss, chiefly quartz–feldspar–mica with dark biotite/amphibole bands

AI-generated identification · may be incorrect

Typically 6–7 Mohs; gray, tan, and black compositional banding, with a granular texture and dull to slightly glassy luster. The rounded shape is from water abrasion; individual mineral cleavage is visible rather than a uniform rock cleavage.

Identified August 9, 2026More metamorphic →

Explore Banded gneiss pebble in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed when preexisting igneous or sedimentary rock underwent high-grade metamorphism, causing minerals to recrystallize and segregate into bands, commonly during Precambrian–Paleozoic mountain building. The specimen was later eroded into a stream or beach pebble.

Uses & applications

Used as aggregate, dimension stone, landscaping rock, and decorative polished stone; this small specimen has modest collector value.

Geological facts

The alternating light and dark layers are compositional foliation, not sedimentary bedding, and can record intense continental collision and deep-crustal pressure.

Field identification & locations

Identify it by persistent light quartz/feldspar bands alternating with dark mica or amphibole, granular crystals, and streaked foliation; common in glaciated terrains, mountain belts, river gravels, and beaches. Value is usually $2–$15 for a common pebble, or $20–$75 if unusually patterned and polished.